1. Field of the Invention
The present invention relates to an inkjet printing apparatus, wherein heat is generated by applying a drive pulse to heat generating elements provided for a print head, and is employed for the ejection of ink to perform printing, and to a driving method for driving the heat generating elements.
2. Description of the Related Art
As a recent trend, inkjet printing apparatuses, which perform printing by ejecting ink from print heads, are employed as image forming apparatuses for forming images on printing media. Some of these inkjet printing apparatuses employ a printing method whereby heat generating elements are heated by the application of drive pulses, and bubbles are generated on the heat generating elements in ink to perform the ejection of ink onto printing media. For the inkjet printing apparatuses of this type, the heat generating elements may be driven by applying double pulses to perform the ejection of ink. When a double-pulse inkjet printing apparatus drives the heat generating elements, first, the heat generating elements are driven by applying a pulse that is not accompanied by the ejection of ink droplets, then, driving of the heat generating elements is paused, and thereafter, a pulse for the ejection of ink droplets is applied to the heat generating elements that are to be driven.
When the ejection of ink is to be performed by the application of double pulses, the heat generating elements are driven by applying a first pulse that is not accompanied by the ejection of ink droplets, and ink around the heat generating elements is heated. Then, when a pause period has elapsed, the heat generating elements are driven again to eject ink droplets. In a case wherein the application of double pulses is employed in this manner to eject ink, the periods for applying the individual pulses and the period for the paused state are adjusted in accordance with the printing condition.
In Japanese Patent Laid-Open No. 2002-240254, an inkjet printing apparatus is disclosed that employs double pulses for the ejection of ink, and that adjusts the lengths of pulse drive periods and a pause period in accordance with a voltage drop that has occurred when ink is ejected from a plurality of ejection ports by driving heat generating elements in a time-division manner.
The length of the pulse drive periods and the length of the pause period may also be limited depending on the other condition. Especially when the ink ejection frequency is to be increased to raise the printing speed, it is required that the pulse drive periods and the pause period be reduced.
However, when the pulse drive periods and the pause period are merely reduced, there is a possibility that a desired volume of ink will not be ejected. Further, in a case wherein the pulse drive periods are extended to ensure a desired volume of ink will be ejected, there is a possibility that the total of the pulse drive periods and the pause period may not fall within a required period of time. In such a case, the ink ejection frequency cannot be increased, and a desired printing speed may not be obtained.